tyring to verify our renderer output with that of OpenGL(only perspective projection0


OS: Windows NT.
I am trying to verify our (3d)raycaster output by comparing the bounding box of our rendered output with OpenGl output image’s bounding box. I need this checking only for verifying if our “perspective projection” is fine.

For simplicity consider I have a cube of (256x256x256) having same intensity, rotated by -20 degrees about z axis and being displayed in a window(in our program) I need program in OpenGL which does the same and which can give me bounding box of the 2d output image. I was successful in creating cube in OpenGL and displaying with ortho projection.

  • but setting the size of the cube to 256x256x256 in OpenGL is not known to me. How do I do that? Curently I use glBegin(GL_QUADS) …;…; for all 6 sides of the cube. Looks like glVertex3f only takes in normalised values w.r.t windows. I need to set the size of the cube exactly!
    *Also rotating about z axis by -20 degrees. I tried using glRotatef(-20, 0, 0,1); Is this right?
    *I have my nearVal, farVal and fieldOfView for setting the perspective projection… I currently use ortho projection in OpenGL. How do I set perspective projection.

Thanks for any hints or help.

for setting up your projective projection use:

gluPerspective(GLdouble fovy, GLdouble aspect, GLdouble zNear, GLdouble zFar)

fovy: field of view in degree in y direction
aspect: aspect ratio (width/height of your viewport)
zNear, zFar: NearPlane, FarPlane

i don’t really understand your glVertex problems

for the front side ouf you cube your code should look like this:


glVertex takes world-coordinates as input
so if you want a 256x256x256 cube the above code gives you the front side the other sides you should be able to figure out yourself

btw remember that all vertices have to be specified in the correct order (default is counter-clockwise)

your rotation should work the way you do it

if you have any more problems don’t be shy just ask

hope this helps

p.s.:if you want your cube in wireframe mode use glPolygonMode(GL_FRONT_AND_BACK, GL_LINE) - (as you said this cube shall be a bounding box)